UnavailableError：找到7个根错误并使用TPU，我收到此错误如何解决

如何解决UnavailableError：找到7个根错误并使用TPU，我收到此错误如何解决

from tensorflow.keras.callbacks import ModelCheckpoint,CSVLogger
checkpointer = ModelCheckpoint(filepath='/content/drive/My Drive/Covid-Detection-using-Lung-Xray-Images-master/cdac/Saved/Checkpoint/modelfinal0_100.{epoch:02d}.hdf5',verbose=1,save_best_only=True,monitor = 'val_loss')
csv_logger = CSVLogger('/content/drive/My Drive/Covid-Detection-using-Lung-Xray-Images-master/cdac/Saved/Log/model0.log')

history=model.fit_generator(
    train_generator,steps_per_epoch = train_generator.samples // batch_size,validation_data = validation_generator,validation_steps = validation_generator.samples // batch_size,epochs = 20,callbacks=[csv_logger,checkpointer])

model.save('/content/drive/My Drive/Covid-Detection-using-Lung-Xray-Images-master/cdac/model/model_final_100v2.hdf5',overwrite=True,include_optimizer=True)

在google collab中运行此命令后，出现错误。我使用TPU运行此程序，该程序与使用X射线肺部图像进行Covid19检测有关。它分为正常，肺炎和Covid 3类。我在此代码的前面部分使用驱动器准备数据并提取了zip文件。文件路径已正确给出。请帮忙。预先感谢

错误：

Epoch 1/20
---------------------------------------------------------------------------
UnavailableError                          Traceback (most recent call last)
<ipython-input-17-ae8b80faaa4d> in <module>()
     10     validation_steps = validation_generator.samples // batch_size,11     epochs = 20,---> 12     callbacks=[csv_logger,checkpointer])
     13 
     14 model.save('/content/drive/My Drive/Covid-Detection-using-Lung-Xray-Images-master/cdac/model/model_final_100v2.hdf5',include_optimizer=True)

14 frames
/usr/local/lib/python3.6/dist-packages/six.py in raise_from(value,from_value)

UnavailableError: 7 root error(s) found.
  (0) Unavailable: {{function_node __inference_train_function_41676}} failed to connect to all addresses
Additional GRPC error information from remote target /job:localhost/replica:0/task:0/device:CPU:0:
:{"created":"@1597873146.970016559","description":"Failed to pick subchannel","file":"third_party/grpc/src/core/ext/filters/client_channel/client_channel.cc","file_line":3948,"referenced_errors":[{"created":"@1597873146.808044681","description":"failed to connect to all addresses","file":"third_party/grpc/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc","file_line":394,"grpc_status":14}]}
     [[{{node MultiDeviceIteratorGetNextFromShard}}]]
     [[RemoteCall]]
     [[IteratorGetNextAsOptional]]
     [[strided_slice_57/_252]]
  (1) Unavailable: {{function_node __inference_train_function_41676}} failed to connect to all addresses
Additional GRPC error information from remote target /job:localhost/replica:0/task:0/device:CPU:0:
:{"created":"@1597873146.970016559","grpc_status":14}]}
     [[{{node MultiDeviceIteratorGetNextFromShard}}]]
     [[RemoteCall]]
     [[IteratorGetNextAsOptional]]
     [[strided_slice_91/_288]]
  (2) Unavailable: {{function_node __inference_train_function_41676}} failed to connect to all addresses
Additional GRPC error information from remote target /job:localhost/replica:0/task:0/device:CPU:0:
:{"created":"@1597873146.970016559","grpc_status":14}]}
     [[{{node MultiDeviceIteratorGetNextFromShard}}]]
     [[RemoteCall]]
     [[IteratorGetNextAsOptional]]
     [[strided_slice_126/_166]]
  (3) Unavailable: {{function_node __inference_train_function_41676}} failed to connect to all addresses
Additional GRPC error information from remote target /job:localhost/replica:0/task:0/device:CPU:0:
:{"created":"@1597873146.970016559","grpc_status":14}]}
     [[{{node MultiDeviceIteratorGetNextFromShard}}]]
     [[RemoteCall]]
     [[IteratorGetNextAsOptional]]
     [[TPUReplicate/_compile/_4505907264126063010/_4/_238]]
  (4) Unavailable: {{function_n ... [truncated]